add multi selection based on CultriX's PR

See https://huggingface.co/spaces/mlabonne/Yet_Another_LLM_Leaderboard/discussions/9/files

app.py

@@ -161,6 +161,10 @@ def main():
                     height=int(len(df) * 36.2),
                 )
 
+                selected_models = st.multiselect('Select models to compare', df['Model'].unique())
+                comparison_df = df[df['Model'].isin(selected_models)]
+                st.dataframe(comparison_df)
+                
                 # Add a button to export data to CSV
                 if st.button("Export to CSV"):
                     # Export the DataFrame to CSV